The machine in question is a module with synchronised parallel movements so that combined together they generate three co-ordinate axes in the tool or clamp. Its application is preferably focused on transfer machines, machining centres, agile modules and/or component manipulation applications.
This invention is designed as the next generation of machines which, applied in different layouts or utilities, can facilitate the adjustment of certain machinery manufacturing firms to the demand of such demanding sectors as the motor vehicle sector, thus maintaining or improving their competitive capacity on this market which, over the last few years has been directly or indirectly consuming more than 50% of the machine-tool production.
The current demands of this type of market are forcing the machinery manufacturers to adopt more and more creative constructive solutions that differ from the traditional machines, as these are within their limit optimisation for the majority of the basic design parameters.
In this regard the parallel kinematic solutions, that is, machines with drives that work simultaneously instead of decoupled, provide a qualitative solution for many of the existing problems.
One of the first applications of machines with non-Cartesian architecture is based on the parallel kinematics of the Stewart platform for the manufacture of air simulators (end of the sixties).
In the case of this machine: the head is mounted on a platform supported by six telescopic shafts. The shafts are directly connected to the fixed table. The length of the telescopic shafts determines the position of the head, which moves with 6 degrees of freedom (3 traverses and 3 rotations) where the maximum permissible angle is restricted to 30xc2x0.
As a result of this, the Cartesian axes do not appear as such and they only exist in a virtual way in the control system.
The main difference with the Cartesian mechanisms lies in that there is not just one kinematic chain that transmits all the forces, but that in the case of six shafts, these form six xe2x80x9cparallelxe2x80x9d kinematic chains where the forces are distributed.
Here, each shaft defines a degree of freedom and transmits only purely tractive or compressive forces in the direction of the position of the shaft.
In the parallel mechanisms, no shaft xe2x80x9cdrawsxe2x80x9d the other. And therefore, the mass to be moved is considerably less than that of the traditional machines. The forces are distributed over all the shafts. Therefore, the parallel mechanisms with very small masses to be moved can be manufactured in a very rigid way. The combination of small masses to be moved and high rigidity means that the parallel mechanisms are of special interest in high speed machining.
However, the telescopic shafts are difficult to design with sufficient rigidity. In addition, the working area of the hexapod is always symmetrical in rotation and cannot be designed arbitrarily. In addition, the hexapods are relatively large in existing prototypes.
Currently, an attempt is being made to develop solutions whose kinematics has the advantages of the parallel structures but which avoid some of the disadvantages. Shafts mounted on slides, which move on parallel guides, linear motors that act as drives.
The applicant has developed a module with parallel kinematic movement, which presents the following characteristics and advantages respect to known devices.
This invention is comprised of several structural elements:
The passive structure, without drives, which supports the movements on a plane, is based on one or several kinematic shears articulated on at least one edge. The aim of this mobile structure is to absorb stress in the three Cartesian axes and in the three moments.
A fixed structure, which supports the whole machine, is joined to this passive structure on one side and on the other there is a mobile structure that carries the head with the relative guides.
On the one hand, there are some xe2x80x9carmsxe2x80x9d which are joined on the one hand to the fixed structure and on the other to the mobile structure that carries the head or the clamp by means of cardan joints or by means of spherical ball joints. These active arms are the ones where the drives are implemented.
The distribution in the space of the anchorage points to the fixed structure, to the mobile structure and to the arms must be calculated depending on the rigidity, speed and acceleration that the tool is to be provided with.
This invention presents a series of very important advantages both from the structural viewpoint and from the kinematic and dynamic viewpoint.
The configuration described above presents minimal rigidities at any point of its work volume that are three times greater than those of any traditional machine. This is due to the combination of the good position of mobile structural elements in the space joined to the passive elements.
The work volume of the machine in mm3 is more than twice the work volume of a machine with the same working cube.
The machine volume ratio occupied respect to the working cube that the tool or clamp can reach is similar to that of the most demanding machines with serial drives and much greater than that of the existing machines with parallel drives.
From the viewpoint of its use in sectors where the machine width is essential as production lines are configured and therefore the minimum transfer distance between modules is critical, it can be said that this invention optimises the width measurement respect to the course requested in that dimension as for machine measurements of 1 we obtain possible courses of 0.8.
In the most simple configuration of the invention the number of drives used is the same as the number of the shafts of the movement controlled, in this aspect it is clearly better than the traditional parallel kinematic solutions with six arms and five shafts.
The combination of xe2x80x9cbarxe2x80x9d type active structural elements with the articulated passive structures permits considerably greater bending moments to be supported than the rest of solutions which only have three xe2x80x9cbarxe2x80x9d type structures.
The weight that the drives have to move is considerably less than that of a traditional machine with similar course movements.
The number of components that comprise this machine is considerably less than the number of components of a traditional machine so both its final cost and the installation are substantially reduced.
As there are no structural elements such as carriages and intermediate parts the necessary machining and therefore the cost is considerably reduced.
The distribution of the possible work volume for the machine makes it possible to circumscribe an orthogonal working cube but it leaves extra-courses free that can be used to carry out collateral activities such as tool changes, tool checks, etc., without having to invade the part area.
The most complex variant of the machine, with a supplementary drive, enables the relative rotation of the structure, which encircles the head support around axis Z to be controlled. Thus positions with greater rigidity can be achieved.
The layout of the machine in the space related to the fixed structure can vary without affecting the performance of the invention at all. This, however, can allow the client to choose greater courses in some of the axes at random without any additional cost for the manufacturer.